🏃‍♂️ Doing Cardio In Fasted State Causes Muscle Loss (2024)

Burn Fat & Increase Metabolism

The other day I got asked the following question:

Dr. Sam – I want to lose fat and gain muscle. I’m doing intermittent fasting and sometimes a ketogenic diet. However, my question is about doing cardio on an empty stomach, first thing in the morning. I hear it’s the best way to lose fat – can you please tell me the real truth?

This is a great question because it’s a very popular topic and one that I used to believe in myself when I was younger.

Theories on Cardio and Fasting

For years, many experts will tell you that the best way to lose fat is to do cardio exercise first thing in the morning, on an empty stomach, after an overnight fast.


The “theory” for this is that your glycogen stores were depleted during your sleep. So, there was no “sugar” or “carbs” to burn off and thus, the cardio exercise would go directly into fat-burning mode.

So you’re saving time and burning more fat.

However, doing cardio after a meal or when you’re not depleted, means that you FIRST have to burn off all the sugar, before you can go into burning off the fatty acids.

So, this meant that the cardio session was just burning off the food you ate, NOT actually burning off body fat. It wasn’t very efficient.

And guess what, this made perfect sense to me.

My Own Experience with Fasting

So, years ago, I would get up in the morning, after not eating for at least 8-10 hours. I’d drink some water and then go for a jog or head on over to the gym and do some incline treadmill or ride the bike or something similar.

I’d do this for at least 30 minutes and work up a nice sweat. Plus with the extra endorphins from the intense cardio, I was super energized and happy. It was a natural high. I felt great. It was a nice way to start the day.

Then I’d come home, I’d take a shower, and I’d wait about an hour before I’d eat, so the “fat-burning” from the cardio session would continue.

And the good news is that I did lose weight and I lost it quickly.

Unfortunately, I lost a lot of muscle in the process.

Looking at just the scale, I was kicking ass. I was losing weight.

Scale fasted state

But looking in the mirror, how my clothes fit and how I was performing in the gym when lifting weights – well, for sure I was losing muscle.

I was slowly getting smaller and weaker.

In 2 months, I lost about 10 lbs. But looking in the mirror, it looked like I only lost 2-3 lbs of fat. I looked flat, stringy, and basically, I had that dreaded “skinny/fat” look.

So I figured maybe I wasn’t eating enough food, so I increased my calories.

The weight loss stopped, but I didn’t look any better.

The bottom line was that I lost weight, but a lot of it was valuable muscle.

So, why did this happen? Did I do something wrong?

How Cardio Affected My Body…

Well, the reason is that the cardio was stressing my body. It was too intense. I had no food in my system, so my body thought something must be wrong. He’s hungry and he’s running away from something.

So, it wants to protect and it goes into survival mode.

It increases stress hormones, such as cortisol. It’ll then lower thyroid levels, to slow down your metabolism. It also messes up with your sex hormones.


I know this for a fact because I started doing both saliva and blood tests to see what was going on. My cortisol levels were like double the high range.

And, my testosterone had dropped in the process as well.

And there were other negative changes in other hormones.

And over the years, I’ve seen this happen over and over again with other people. And it happens to certain people and body types much worse.

Women, for example, lose muscle more than men doing intense cardio in a fasted state.

Skinnier, “ectomorphs” for sure lose a lot more muscle, as well.

People who lift weights, lose muscle as well.

The people that can do intense cardio in a fasted state tend to be genetically muscular people – mesomorph or endomorph who put on fat quickly.

Also, people taking steroids can get away with this easily.

What Is Best To Do?

So, knowing what I know now, I would do things differently.

I would NEVER do intense cardio, any time of the day. This means NO running, jogging, biking, etc. Only a few genetically gifted people can do this and not lose muscle.

If you want to do cardio in a fasted state in the morning, that’s fine. But do a 15-30 min brisk walk. Just enough that you’re breathing hard, but you can still carry a conversation. NO intense cardio, running, jogging, etc.


Instead of doing long cardio sessions, such as 30-60 min brisk walks, it’s best to do multiple smaller sessions. For example, 10-15 minutes, 3x daily. Before or after a meal.

Doing the above will allow you to burn more fat, NOT lose muscle and most importantly, turn on your fat-burning hormones and increase your metabolism, all day long.

It’s easier to do. It’s less stressful. You can do it any time, any place and it won’t cost you anything.

More importantly, it won’t screw up your hormones and accelerate aging.

And if you want more details about how to naturally turn on your fat-burning hormones all day long, make sure you visit this special link.

You’ll also discover why 93% of diet and exercise programs fail and how to quickly fix it.

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